Lateralized cognitive functions in Parkinson’s patients: A behavioral approach for the early detection of sustained attention deficits

Age and beta amyloid deposition impact gait speed, stride length, and gait smoothness while transitioning from an even to an uneven walking surface in older adults

BACKGROUND

Capturing a measure of movement quality during a complex walking task may indicate the earliest signs of detrimental changes to the brain due to beta amyloid (Aβ) deposition and be a potential differentiator of older adults at elevated and low risk of developing Alzheimer's disease. This study aimed to determine: 1) age-related differences in gait speed, stride length, and gait smoothness while transitioning from an even to an uneven walking surface, by comparing young adults (YA) and older adults (OA), and 2) if gait speed, stride length, and gait smoothness in OA while transitioning from an even to an uneven walking surface is influenced by the amount of Aβ deposition present in an OA's brain.

METHODS

Participants included 56 OA (>70 years of age) and 29 YA (25-35 years of age). In OA, Aβ deposition in the brain was quantified by PET imaging. All participants completed a series of cognitive assessments, a functional mobility assessment, and self-report questionnaires. Then participants performed two sets of walking trials on a custom-built walkway containing a mixture of even and uneven surface sections, including three trials with a grass uneven surface and three trials with a rocks uneven surface. Gait data were recorded using a wireless inertial measurement unit system. Stride length, gait speed, and gait smoothness (i.e., log dimensionless lumbar jerk) in the anteroposterior (AP), mediolateral (ML), and vertical (VT) directions were calculated for each stride. Outcomes were retained for five stride locations immediately surrounding the surface transition.

RESULTS

OA exhibited slower gait (Grass: p < 0.001; Rocks: p = 0.006), shorter strides (Grass: p < 0.001; Rocks: p = 0.008), and smoother gait (Grass AP: p < 0.001; Rocks AP: p = 0.002; Rocks ML: p = 0.02) than YA, but they also exhibited greater reductions in gait speed and stride length than YA while transitioning to the uneven grass and rocks surfaces. Within the OA group, those with greater Aβ deposition exhibited decreases in smoothness with age (Grass AP: p = 0.02; Rocks AP: p = 0.03; Grass ML: p = 0.04; Rocks ML: p = 0.03), while those with lower Aβ deposition exhibited increasing smoothness with age (Grass AP: p = 0.01; Rocks AP: p = 0.02; Grass ML: p = 0.08; Rocks ML: p = 0.07). Better functional mobility was associated with less smooth gait (Grass ML: p = 0.02; Rocks ML: p = 0.05) and with less variable gait smoothness (Grass and Rocks AP: both p = 0.04) in the OA group.

CONCLUSION

These results suggest that, relative to YA, OA may be adopting more cautious, compensatory gait strategies to maintain smoothness when approaching surface transitions. However, OA with greater Aβ deposition may have limited ability to adopt compensatory gait strategies to increase the smoothness of their walking as they get older because of neuropathological changes altering the sensory integration process and causing worse dynamic balance (i.e., jerkier gait). Functional mobility, in addition to age and Aβ deposition, may be an important factor of whether or not an OA chooses to employ compensatory strategies to prioritize smoothness while walking and what type of compensatory strategy an OA chooses.

Moderating effects of uric acid and sex on cognition and psychiatric symptoms in asymmetric Parkinson's disease

BACKGROUND

Non-motor symptoms are an important early feature of Parkinson's disease (PD), encompassing a variety of cognitive and psychiatric symptoms that seem to manifest differently depending on motor symptom asymmetry. Different factors, such as uric acid (UA) and sex, seem to influence cognitive and psychiatric expression in PD, however their interplay remains to be better understood.

METHODS

Participants taking part in the Parkinson's Progression Marker Initiative were studied based on the side of motor symptom asymmetry and sex. Three-way interaction modeling was used to examine the moderating effects of sex and UA on cognitive functions and psychiatric symptoms.

RESULTS

Significant three-way interactions were highlighted at 1-year follow-up between motor symptom asymmetry, UA and sex for immediate and long-term memory in female patients exhibiting predominantly left-sided motor symptoms, and for processing speed and sleepiness in female patients exhibiting predominantly right-sided motor symptoms. No significant interactions were observed for male patients. Moreover, female patients exhibiting predominantly right-sided motor symptoms demonstrated lower serum UA concentrations and had overall better outcomes, while male patients with predominantly right-sided motor symptoms demonstrated particularly poor outcomes.

CONCLUSIONS

These findings suggest that in the earliest stages of the disease, UA and sex moderate cognitive functions and psychiatric symptoms differently depending on motor asymmetry, holding important clinical implications for symptom management in patients.

Biomarkers and non-motor symptoms as a function of motor symptom asymmetry in early Parkinson's disease

INTRODUCTION

The longitudinal trajectories of cognitive-neuropsychiatric symptoms from the early stages of Parkinson's disease, as a function of motor symptom asymmetry at the onset of the disease, remain to be fully explored. Moreover, the relationship to biomarkers warrants further investigation.

METHODOLOGY

Non-motor and biospecimen data from 413 patients with Parkinson's disease, dissociating predominantly left-sided motor symptoms patients (n = 179), predominantly right-sided motor symptoms patients (n = 234), and matched healthy controls (n = 196), were extracted from the Parkinson's Progression Marker Initiative database during a 3-Year follow-up. Non-parametric and conservative corrections for multivariate comparisons were carried out on neuropsychiatric and biomarker data.

RESULTS

A decline for global cognitive efficiency scores in predominantly right-sided motor symptoms patients was observed, whereas depressive and anxiety symptoms were greater overtime for predominantly left-sided motor symptoms patients. Biomarker analysis revealed that predominantly right-sided patients expressed decreased levels of total-tau and phospho-tau over time, while left-sided patients didn't differ from healthy controls.

CONCLUSION

From the early course of the disease, the existence of different clinical phenotypes is proposed, associated to emerging evidences of distinct pathological pathways and a left-hemispheric vulnerability for cognitive decline.

Compensatory movement strategies differentially affect attention allocation and gait parameters in persons with Parkinson’s disease

Persons with Parkinson’s disease (PwP) are advised to use compensatory strategies such as external cues or cognitive movement strategies to overcome gait disturbances. It is suggested that external cues involve the processing of sensory stimulation, while cognitive-movement strategies use attention allocation. This study aimed to compare over time changes in attention allocation in PwP between prolonged walking with cognitive movement strategy and external cues; to compare the effect of cognitive movement strategies and external cues on gait parameters; and evaluate whether these changes depend on cognitive function. Eleven PwP participated in a single-group pilot study. Participants walked for 10 min under each of three conditions: natural walking, using external cuing, using a cognitive movement strategy. Attention and gait variables were extracted from a single-channel electroencephalogram and accelerometers recordings, respectively. Attention allocation was assessed by the% of Brain Engagement Index (BEI) signals within an attentive engagement range. Cognitive function was assessed using a neuropsychological battery. The walk was divided into 2-min time segments, and the results from each 2-min segment were used to determine the effects of time and condition. Associations between cognitive function and BEI signals were tested. Findings show that in the cognitive movement strategy condition, there was a reduction in the % of BEI signals within the attentive engagement range after the first 2 min of walking. Despite this reduction the BEI did not consistently differ from natural and metronome walking. Spatiotemporal gait variables were better in the cognitive movement strategy condition relative to the other conditions. Global cognitive and information processing scores were significantly associated with the BEI only when the cognitive movement strategy was applied. In conclusion, the study shows that a cognitive movement strategy has positive effects on gait variables but may impose a higher attentional load. Furthermore, when walking using a cognitive movement strategy, persons with higher cognitive function showed elevated attentive engagement. The findings support the idea that cognitive and attentional resources are required for cognitive movement strategies in PwP. Additionally, this study provides support for using single-channel EEG to explore mechanistic aspects of clinical interventions.

A novel virtual reality approach for functional lateralization in healthy adults

Functional lateralization relates to a natural asymmetry in the dominance right or left body side, and is a fundamental principle of the brain. The hemispheres of the brain control the contralateral body side, and show subtle, yet striking, anatomical asymmetries and functional lateralization. Innovative technologies, including Virtual Reality (VR), are entering the areas of experimental research, modeling and simulation related to the study of lateralization, with new perspectives of different applications in modern medical practice. Researchers/clinicians note that there are fewer VR studies with healthy participants, and which are important in evaluating/interpreting clinical outcomes, and testing the usefulness, limitations, and sensitivity of VR. The presented influence of the domination of upper/lower limbs on the performance of VR exercises was studied in healthy right-handed adults. Virtual testing sessions were performed independently with both/ dominant/ non-dominant hands, and the similar VR sessions were conduced on a Wii Balance Board (WBB) with the choice of body side, at different levels of the difficulty. The obtained results are consistent with other studies which show that cognitive-motor training in VR with the WBB platform is a very sensitive and promising tool for recognizing/assessing functional asymmetries of the right-left body side not only in disturbed lateralization, but also in the test training of healthy subjects.

The α-Synuclein Origin and Connectome Model (SOC Model) of Parkinson's Disease: Explaining Motor Asymmetry, Non-Motor Phenotypes, and Cognitive Decline

A new model of Parkinson's disease (PD) pathogenesis is proposed, the α-Synuclein Origin site and Connectome (SOC) model, incorporating two aspects of α-synuclein pathobiology that impact the disease course for each patient: the anatomical location of the initial α-synuclein inclusion, and α-synuclein propagation dependent on the ipsilateral connections that dominate connectivity of the human brain. In some patients, initial α-synuclein pathology occurs within the CNS, leading to a brain-first subtype of PD. In others, pathology begins in the peripheral autonomic nervous system, leading to a body-first subtype. In brain-first cases, it is proposed that the first pathology appears unilaterally, often in the amygdala. If α-synuclein propagation depends on connection strength, a unilateral focus of pathology will disseminate more to the ipsilateral hemisphere. Thus, α-synuclein spreads mainly to ipsilateral structures including the substantia nigra. The asymmetric distribution of pathology leads to asymmetric dopaminergic degeneration and motor asymmetry. In body-first cases, the α-synuclein pathology ascends via the vagus to both the left and right dorsal motor nuclei of the vagus owing to the overlapping parasympathetic innervation of the gut. Consequently, the initial α-synuclein pathology inside the CNS is more symmetric, which promotes more symmetric propagation in the brainstem, leading to more symmetric dopaminergic degeneration and less motor asymmetry. At diagnosis, body-first patients already have a larger, more symmetric burden of α-synuclein pathology, which in turn promotes faster disease progression and accelerated cognitive decline. The SOC model is supported by a considerable body of existing evidence and may have improved explanatory power.